This disclosure relates generally to data storage systems, and more particularly, but without limitation, to the use of meta data to decrease time associated with reading data from data storage systems.
Many data storage systems include mirroring or similar utilities for copying one logical volume to another. A logical volume may be copied, for instance, during routine backup (a.k.a. snap-shot) operations. A logical volume may also be copied when hardware is replaced, for example when a disk drive is replaced with a disk drive having a larger storage capacity. Moreover, a logical volume may be copied to redistribute data from failed or failing hardware, for instance in a Redundant Array of Independent Disks (RAID) configuration. Such mirroring or similar utilities may be invoked on a manual or automatic basis.
FIG. 1 is a flow diagram of a logical volume copy process, according to the prior art. A copy is essentially a read followed by a write. As indicated therein, the process begins in a step 105 by receiving a logical volume copy command. Next, in step 110, the process selects a first portion of the logical volume. Then, in step 115, the process reads data associated with the selected portion of the logical volume. Next, in step 120, the process writes data associated with the selected portion of the logical volume. Then, in conditional step 125, the process determines whether all portions of the logical volume have been copied. Where the result of conditional step 125 is in the negative, the process returns to step 110 to select a next portion of the logical volume. Where the result of conditional step 125 is in the affirmative, the process terminates in step 130.
Known systems and methods for mirroring or copying data have many disadvantages, however. For instance, in enterprise class data storage systems that contain large amount of data, known copying schemes may require hours or days to complete. Such lengthy copying consumes limited resources during data back-up operations. In addition, lengthy copying adversely affects the Mean Time to Repair (MTTR) and/or may risk data loss in instances of hardware failure. Moreover, known copying schemes may require impractical amounts of time to upgrade a data storage system.